1. Field of the Invention
This invention generally relates to monitoring of water quality, and more particularly to an automated system for and method of monitoring the quality of water at one or more ground water sampling sites.
2. Description of the Related Art
Determining the quality of water by monitoring one or more of its properties and constituents is well known, and at present is generally accomplished by one of two methods.
The first method is a manual method in which a field technician is deployed to draw samples from a well. The samples are then tested on-site in accordance with established protocols or are transported to a laboratory for analysis. The following publications disclose manual methods of this type: Gilliam et al, Groundwater Monitoring and Sample Bias, Environmental Affairs Department, American Petroleum Institute, page 206, June 1983; Driscoll, Groundwater and Wells, 2nd edition, page 1108, 1986; and Koterba et al, "Ground-Water-Data-Collection Protocols and Procedures for the National Water-Quality Assessment Program--Collection and Documentation of Water-Quality Samples and Related Data," U.S. Geological Survey Open-File Report 95-399, page 113, 1995.
Manual methods for determining ground water quality have proven to be inherently burdensome and inefficient. For example, as noted in the article "Sampling Frequency for Monitoring the Actual State of Ground Water Systems," Journal of Hydrology Volume 180, pages 301-318, 1996 by Zhou, the necessity of having to deploy one or more field technicians to a site to retrieve test samples has proven to be economically unsound, and the costs associated therewith only tend to increase in proportion to the number of wells tested within a given sampling site.
Manual methods are undesirable also because personnel shortages, inclement weather, and other factors limit the frequency with which samples can be taken,--i.e., typically water samples can be tested only once or twice a month in areas having a high concentration of sites. Consequently, changes in water quality that take place over short periods of time, for example, due to surges of effluent and other contaminating influences into the water table, will often go undetected. Thus, manual methods are inherently unreliable as research tools. See the Zhou article noted above, as well as Johnson et al, "Reducing the Sampling Frequency of Groundwater Monitoring Wells", Environmental Science and Technology, Volume 30, no. 1, pages 355-358, 1996, for a more in-depth discussion of these and other drawbacks, and of various unsuccessful approaches which have been taken in an attempt to improve the inherent deficiencies of manual ground water quality monitoring methods.
The second method for monitoring water quality is an automated method employing passive techniques. According to this method, a data logger controls a probe in a well to make measurements from which water quality can be determined. Automated methods of this type are disclosed in the article "Automated Monitoring and Interactive Data Evaluation for a Gravel Aquifer in Central London," Journal of Engineering Geology, Volume 25, note 4, pages 351-358, 1992, by Evans.
Automated systems have, in other monitoring applications, outperformed their manual counterparts. Perhaps most notably, automated systems are less expensive to operate, mainly because use of a data logger relieves field technicians of the job of having to capture the samples to be tested. Automated systems also advantageously may be programmed to take a greater frequency of measurements as compared with measurements taken by manual methods. The data collected by such automated systems are often electronically stored, and thus have proven to be comparatively easier to use. All of these advantages translate into lower costs, and a broader statistical basis from which water quality at a given site can be determined.
Some automated systems have been equipped with diagnostic feedback, which plays a pivotal role in increasing system reliability. For these and other advantages see, for example, Fink et al, "Computerized System Simplifies Well Testing/Monitoring", World Oil, Volume 216, No. 6, pages 109-110, 1995; Church et al, "Effectiveness of Highway-Drainage Systems in Preventing Contamination of Ground Water by Road Salt, Route 25, Southeastern Massachusetts-Description of Study Area, Data Collection Programs, and Methodology," U.S. Geological Survey Open-File Report 96-317, 1996; Igarashi et al, "Continuous Monitoring of Groundwater Radon for Evaluating Chemical and Structural Properties and Fluid Flow Variations of Shallow Aquifer Systems," Journal of Science of the Hiroshima University 10, No. 2, pages 349-356, 1995; Riley et al, "Automated Water Quality Monitoring and Control in Aquaculture," World Aquaculture 26, No. 2, pages 35-37, 1995; and Chiron et al, "Automated Sample Preparation for Monitoring Groundwater Pollution by Carbamate Insecticides and Their Transformation Products," Journal of AOAC International 78, No. 6, pages 1346-1352, 1995.
Known automated ground water monitoring methods passively record measurements in a stagnant well bore and so do not take into consideration the advantages resulting from purging a well prior to recording a measurement. The deleterious effects of this oversight are noted in "Manual of Ground-Water Quality Sampling Procedures," National Water Well Association, 1981, by Scalf et al. This article discloses that the composition of water in and proximate to a well is likely not representative of the groundwater generally in the area. The article "Field Evaluation of Well Flushing Procedures," American Petroleum Institute, 1985, by Gillham et al, discloses that water standing in a polyvinylchloride (PVC) well for as short a period of time as three weeks has demonstrated changes in inorganic chemistry sufficient to cause this water to significantly deviate in quality from groundwater in surrounding locations.
The chemical changes that take place in stagnant borehole water over time are expounded upon in the article "Ground-Water Sampling," in Practical Handbook of Ground-Water Monitoring, 1991, by Herzog et al. In Herzog, it is disclosed that temperature, pH, oxidation reduction potentials, and dissolved solids content of stagnant borehole water are adversely affected by influences such as rust and scale on well construction materials, bacteria activity in the well, interactions that take place with the atmosphere, volatilization of organic compounds therein, and effervescence of dissolved gasses in the water over an extended period of time.
In view of these chemical changes, it is generally agreed that a well should be purged of contaminated water prior to the taking of a water quality measurement therein. The exact method for optimally purging a well, however, is still the subject of debate. See Robin et al, "Field Evaluation of Well Purging Procedures," Ground Water Monitoring Review, Fall 1987, pages 85-93. Known automated methods fail to even address these purging concerns, consequently, their measurements are often inaccurate.
Known automated methods also have various physical limitations. In the above-mentioned article by Evans, it is pointed out that the size of the pressure transducers and other probes used by known automated water quality monitoring methods limits the minimum diameter of the wells in which they are installed. For at least the foregoing reasons, known automated systems have proven to be less than optimal for monitoring water quality.
Other systems and methods have been developed for sampling water from a well. U.S. Pat. No. 5,224,389 to Jensen, for example, discloses a method of obtaining a sample of groundwater from a well. In the Jensen method, water is pumped from a well until a predetermined criterion (e.g., a minimum variation in electrical conductivity) is satisfied, at which time a sample of what is considered to be substantially non-contaminated water is taken from additional water pumped from the well. The sample is then removed from the well site so that it may be analyzed to determined the quality of water therein.
Jensen is basically a manual system. For example, to implement the Jensen system, a field technician is required to move a mobile sampling unit to the site, and then to turn on the system to initiate purging and sampling. The technician must then remove the unit from the site and take the sample collected therein to a laboratory for testing. The substantial human involvement required to employ the Jensen approach thus makes Jensen as deficient as the conventional systems discussed above.
U.S. Pat. No. 5,553,492 to Barrett discloses taking periodic water level measurements at a plurality of wells, and then transmitting these measurements to a remote location for processing. The Barrett system, however, fails to take a water quality measurement of any kind. Rather, Barrett merely discloses taking water level measurements for the sole purpose of determining the direction of groundwater flow within a region of interest. Furthermore, Barrett requires at least some degree of human intervention to carry out its objectives. For example, water level measurements taken at a well site are transmitted only upon receipt of a user-initiated request.
U.S. Pat. No. 4,717,473 to Burge discloses a self-contained groundwater sampler which automatically collects a water sample from a well at a programmed time. It is also disclosed that the Burge sampler may be adapted to include a unit for analyzing the chemical or physical make up of a collected sample. The Burge system, however, has a number of drawbacks. First, no purging operation is performed prior to analysis. Thus, measurements obtained by the Burge system will likely be inaccurate for reasons previously noted. Second, the Burge system is limited in that it can collect only one sample at a time, and thus requires servicing before obtaining additional samples.
U.S. Pat. No. 5,259,450 to Fischer discloses a pumping apparatus containing a vented packer for minimizing the amount of water to be purged from a well prior to obtaining a sample therefrom. In order to activate the pump, however, a field technician must install a removably mountable controller at the well site, and then must be deployed to retrieve collected samples.
U.S. Pat. No. 5,490,561 to Cardoso-Neto discloses purging a predetermined quantity of water from a well, collecting a sample, and then returning the purged and sampled water to the well. None of these steps, however, is disclosed as being automated, and so a technician must visit this site as well.
From the foregoing discussion, it is evident that while automated systems and methods have been developed for monitoring the quality of water at a sampling site, such systems and methods still require a substantial degree of human intervention and thus are inherently costly and inefficient. Further, known systems and methods fail to take precautions necessary to prevent collected water samples from being contaminated, and thus measurements derived therefrom are likely to be inaccurate.
A need therefore exists for an automated system and method which monitors the quality of water at a sampling site at regular intervals without human intervention, and which does so in a manner to ensure that the samples being tested are free from contamination, thereby enabling a true and accurate determination of water quality to be made.